#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string>
#include <string.h>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <assert.h>
#include <algorithm>
#include <iomanip>
#include <time.h>
#include <math.h>
#include <bitset>
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#pragma comment(linker, "/STACK:256000000")
using namespace std;
typedef long long int ll;
typedef long double ld;
typedef gp_hash_table<int, int> table;
const int INF = 1000 * 1000 * 1000 + 21;
const ll LLINF = (1ll << 60) + 5;
const int MOD = 998244353;
const int MAX_N = 1000 * 1000 + 228;
struct point {
int x;
int y;
};
bool operator<(const point& a, const point& b) {
return a.x + a.y > b.x + b.y || (a.x + a.y == b.x + b.y && a.x - a.y < b.x - b.y);
}
bool operator==(const point& a, const point& b) {
return a.x == b.x && a.y == b.y;
}
ll n, m;
int k;
map<pair<int, int>, int> costs;
vector<point> points[2];
vector<int> diags[2];
table dp;
inline int calc_cost(int x, int ptr1, int ptr2, map<pair<int, int>, int>::iterator it) {
if (x == n - 1) {
return 0;
} else if (it != costs.end()) {
return it->second;
} else {
int ans = -INF;
if (1 <= ptr1 && ptr1 <= n + n - 1) {
ans = max(ans, dp[ptr1]);
} else {
ans = max(ans, 0);
}
if (1 <= ptr2 && ptr2 <= n + n - 1) {
ans = max(ans, dp[ptr2]);
} else {
ans = max(ans, 0);
}
return ans;
}
}
int main() {
#ifdef CH_EGOR
freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
#else
//freopen("", "r", stdin);
//freopen("", "w", stdout);
#endif
scanf("%lld%lld%d", &n, &m, &k);
n = max(n, m); // magic
for (int i = -2; i <= k; ++i) {
int x, y, c;
if (i == -2) {
x = 0;
y = 1;
c = 0;
} else if (i == -1) {
x = 1;
y = 0;
c = 0;
} else if (i == 0) {
x = 0;
y = 0;
c = 0;
} else {
scanf("%d%d%d", &x, &y, &c);
--x; --y;
costs[{x, y}] = c;
}
for (int dx = 0; dx <= 2; ++dx) {
for (int dy = 0; dy <= 2; ++dy) {
int gox = x - dx;
int goy = y - dy;
if (gox >= 0 && goy >= 0 && dx + dy <= 2) {
points[(gox + goy) & 1].push_back({gox, goy});
diags[(gox + goy) & 1].push_back(gox + goy);
if (gox - goy >= 0) {
points[(gox + goy) & 1].push_back({gox - goy, 0});
diags[(gox + goy) & 1].push_back({gox - goy});
} else {
points[(gox + goy) & 1].push_back({0, goy - gox});
diags[(gox + goy) & 1].push_back(goy - gox);
}
if (gox - goy >= 2) {
points[(gox + goy) & 1].push_back({gox - goy - 2, 0});
diags[(gox + goy) & 1].push_back({gox - goy - 2});
} else if (gox - goy <= -2) {
points[(gox + goy) & 1].push_back({0, goy - gox - 2});
diags[(gox + goy) & 1].push_back(goy - gox - 2);
}
}
}
}
}
int ans = 0;
for (int i = 0; i < 2; ++i) {
dp.clear();
sort(points[i].begin(), points[i].end());
points[i].resize(unique(points[i].begin(), points[i].end()) - points[i].begin());
sort(diags[i].begin(), diags[i].end());
diags[i].resize(unique(diags[i].begin(), diags[i].end()) - diags[i].begin());
reverse(diags[i].begin(), diags[i].end());
int cur_add = 0;
int points_ptr = 0;
for (int j = 0; j < (int)diags[i].size(); ++j) {
int lf = 0;
int rf = 0;
if (diags[i][j] >= n - 1) {
lf = n - ((n + n - 2) - diags[i][j]);
rf = n + ((n + n - 2) - diags[i][j]);
} else {
lf = n - diags[i][j];
rf = n + diags[i][j];
}
if (j != 0) {
ans = (ans + (ll)(diags[i][j - 1] - diags[i][j] - 1) / 2ll * cur_add) % MOD;
}
if (diags[i][j] < n - 1) {
if (dp.find(lf - 2) != dp.end()) {
cur_add = (cur_add - dp[lf - 2]) % MOD;
}
if (dp.find(rf + 2) != dp.end()) {
cur_add = (cur_add - dp[rf + 2]) % MOD;
}
}
vector<pair<int, int>> new_vals;
for ( ;
points_ptr < (int)points[i].size() && points[i][points_ptr].x + points[i][points_ptr].y >= diags[i][j];
++points_ptr) {
int x = points[i][points_ptr].x;
int y = points[i][points_ptr].y;
auto it = costs.find({x, y});
int rl_val = min(
it != costs.end() ? it->second : calc_cost(x, n + x - y + 2, n + x - y, costs.find({x + 1, y})),
it != costs.end() ? it->second : calc_cost(y, n + x - y - 2, n + x - y, costs.find({x, y + 1}))
);
if (lf <= n + x - y && n + x - y <= rf) {
new_vals.push_back({n + x - y, rl_val});
}
}
for (int i = 0; i < (int)new_vals.size(); ++i) {
cur_add = (cur_add - dp[new_vals[i].first]) % MOD;
cur_add = (cur_add + new_vals[i].second) % MOD;
dp[new_vals[i].first] = new_vals[i].second;
}
/*
cerr << "Now " << diags[i][j] << endl;
for (int i = lf; i <= rf; i += 2) {
cerr << dp[i] << " ";
}
cerr << endl;
*/
ans = (ans + cur_add) % MOD;
}
}
if (ans < 0) {
ans += MOD;
}
printf("%d\n", ans);
return 0;
}
